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KernelTrap: Time Sliced CFQ With IO Priorities

"Jens Axboe offered a patch that introduces basic IO priority
support for his time sliced CFQ IO scheduler. Similar in concept to
nice values for the process scheduler, Jens's patch offers '8 basic
io priorities now, 0 being [the] highest prio and 7 the lowest.'
However, whereas nice values adjust a process's priority to CPU
cycles, the IO priority value adjusts a process's priority to disk
IO. With all processes running at the same IO priority, they will
all average the same disk access rate. With process running at
different priorities, the lower the IO priority value the faster
they will access the disk, though the total aggregate bandwidth
will always stay the same..."